Provides an efficient definition of standard permutations,
StPerm, together with an abstract class, Perm, whose
functionality is largely inherited from StPerm using a group
action and the standardization map.

The standardization map. If there is an underlying linear
order on a then st is determined by the unique order
preserving map from [0..] to that order. In any case, the
standardization map should be equivariant with respect to the
group action defined below; i.e., it should hold that

This is not a circular definition as size on StPerm is
implemented independently. If the implementation of st is
slow, then it can be worth while to override the standard
definiton; any implementation should, however, satisfy the
identity above.